Study of the nature of superconductivity in t-PtBi2 and related materials.

• Applicant: Dr. Andrii Kuibarov
• Subject Area: Experimental Condensed Matter Physics
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 555830981

Humanity's reliance on computational technologies has grown significantly in the last two decades, making it hard to imagine our daily lives without them. From simply opening a website to utilizing supercomputers and cutting-edge AI technologies, all of this is powered by semiconductor technologies, which are currently struggling to keep up with computational demands. Quantum computing is one potential approach that could not only address this issue but also revolutionize our computational paradigm entirely. Building fault-tolerant quantum qubits is one of the primary challenges in quantum computing. It has been predicted that Majorana fermions—exotic particles that have been theoretically predicted and sought after for decades in high-energy physics—could be key to solving this problem. The theoretical framework suggests that topological superconductors in solid-state physics can host the Majorana fermions needed for quantum computing. There are generally two approaches to realizing Majorana fermions. The first involves engineering topological superconductors, such as nanowires or heterostructures, where superconductivity is induced through the proximity effect. The second approach relies on the search for materials that are inherently topological superconductors. The biggest challenge with this approach is that intrinsic topological superconductors are extremely rare. This project focuses on one such candidate: trigonal PtBi₂ (t-PtBi₂). As preliminary work for this proposal, we have investigated this material and found that it is a Weyl semimetal that shows signs of surface-only superconductivity. Moreover, our work has shown that superconducting states seemingly manifest only on the topological surface states—Fermi arcs. To our knowledge, this has not been reported in the literature before and is what makes this material so unique and interesting. The main goal of this proposal is to investigate trigonal PtBi₂ and related materials to determine whether PtBi₂ can be considered a topological superconductor or have any practical use. For this, we will employ synchrotron and ultra-high-resolution laser Angle-Resolved Photoemission Spectroscopy (ARPES). More specifically, the end goals can be divided into smaller tasks that we plan to address in the proposal: 1. What is the superconducting pairing symmetry in PtBi₂? (We have preliminary evidence that it’s not s-wave). 2. Can the superconducting critical temperature be increased by modifying the synthesis technique? (We have preliminary evidence that our current samples are inhomogeneous). 3. What is the nature of superconductivity in compounds related to t-PtBi₂, such as PtBi(Se)/Te/Ir? 4. Do the related materials have topological surface states, Fermi arcs? If so, do they play a crucial role in the formation of superconductivity?

• DFG Programme: Research Grants